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| Engineering Reviewer - Electricity and Magnetism Fundamentals |
Electricity and Magnetism Fundamentals
251. The relation between absolute permittivity of air (ε0), absolute permeability of air (μ0) and velocity of light (c) is given by
A. μ0ε0 = c^2
B. μ0ε0 = c
C. 1/μ0ε0 = c
D. 1/μ0ε0 = c^2
252. The dielectric constant of most materials lies between
A. 1 and 10
B. 10 and 20
C. 20 and 50
D. 50 and 100
253. A test charge means a charge of
A. -1 C
B. 1 electron
C. +1 C
D. -20 C
254. Electric lines of force leave or enter the charge surface at an angle of
A. 30̊
B. 45̊
C. 90̊
D. depending upon the angle of launch and entry
255. Electric field intensity is measured in
A. volts/meter
B. Newton/meter
C. Newton-meter
D. Amperes/meter
256. Electric field intensity is a ________.
A. scalar
B. phasor
C. vector
D. variable
257. Electric field intensity at a point due to a given charge ______ if the relative permittivity of the medium decreases.
A. decreases
B. remains unchanged
C. increases
D. becomes zero
258. The electric field intensity between the parallel plate air capacitor is 20 N/C. If an insulating slab of relative permittivity 5 is placed between the plates, then electric field intensity will be
A. 20 N/C
B. 100 N/C
C. 4 N/C
D. 40 N/C
259. The electric flux density is a ________ quantity.
A. phasor
B. vector
C. scalar
D. variable
260. The permittivity of a material is given by one of the following formulas.
A. DE
B. E/D
C. D^2/E
D. D/E
261. Electric field intensity at a point is numerically equal to ________ at that point.
A. potential gradient
B. potential difference
C. dielectric constant
D. the force
262. Three charges of +5 C, -6 C and +9 C are placed inside a sphere. What is the total flux passing through the surface of sphere?
A. 8 C
B. 14 C
C. 20 C
D. -6 C
263. The potential at a point due to a charge is 15 V. If the distance is increased three times, the potential at the point will be
A. 5 V
B. 18 V
C. 45 V
D. 15 V
264. Electric potential is a _______ quantity.
A. scalar
B. phasor
C. vector
D. variable
265. The electric potential at a point in air due to a charge is 21 V. If the air is replaced by a medium of relative permittivity of 3, then electric potential at that point will be
A. 63 V
B. 21 V
C. 7 V
D. 42 V
266. The electric potential across part AB of a circuit is 5 V; point A being at higher potential. If a charge of 5 C moves from A to B, then energy released as
A. 5 joules
B. 25 joules
C. 10 joules
D. 100 joules
267. What is the other name for dielectric strength?
A. Breakdown voltage
B. Electric intensity
C. Potential gradient
D. Dielectric constant
268. Which of the following materials has the highest dielectric strength?
A. Glass
B. Oiled paper
C. Mica
D. Air
269. What is used as the insulating material or dielectric in an electric ion?
A. Oiled paper
B. Mica
C. Paraffin
D. Titanate compound
270. What is used as the dielectric material in high voltage transformers?
A. Mica
B. Paraffin
C. Porcelain
D. Oiled paper
271. One farad equals
A. 1 coulomb/volt
B. 1 newton/coulomb
C. 1 newton-meter
D. 1 volt/second/ampere
272. Which of the following is used by permanent magnets as the magnetic material?
A. iron
B. nickel
C. soft steel
D. hardened steel
273. Which of the following is used by temporary magnets as the magnetic material?
A. Hardened steel
B. Cobalt steel
C. Soft iron
D. Tungsten steel
274. What is the main advantage of temporary magnets?
A. The magnetic flux can be changed.
B. Hysteresis can be decreased.
C. Magnetic materials can be used.
D. Abundance of ferromagnetic material that can be temporarily magnetized.
275. Permanent magnets can be found in
A. electric bells
B. earphones
C. relays
D. dynamic loudspeakers
276. Temporary magnets are commonly employed in
A. electric instruments
B. motors
C. moving coils loudspeakers
D. magnetos
277. The force between two magnetic poles is _______ their pole strengths.
A. directly proportional to
B. the sum of
C. inversely proportional to
D. the product of
278. If the distance between two magnetic poles decreases by 2 times, the force between them
A. decreases two times
B. increases four times
C. increases two times
D. decreases four times
279. The force between two magnetic poles is _____ the relative permeability of the medium.
A. directly proportional to
B. independent of
C. inversely proportional to
D. equal to
280. Two similar poles, each 1Wb, placed 1 m apart in air will experience a repulsive force of
A. 63000 N
B. 63 × 10^-3 N
C. 8 × 10^12 N
D. 796 kN
281. One weber of flux is equal to _______ magnetic lines of force.
A. 10^6
B. 10^10
C. 4π × 10^7
D. 10^8
282. The unit of flux density is
A. Wb/m
B. Tesla
C. At/m
D. N/Wb
283. What is the typical saturation flux density for most magnetic materials?
A. 4 Wb/m^2
B. 5 Wb/m^2
C. 1 Wb/m^2
D. 2 Wb/m^2
284. Magnetic field intensity is a ________ quantity.
A. scalar
B. phasor
C. vector
D. variable
285. The force acting on a pole of 5 Wb is 25 N. What is the intensity of the magnetic field?
A. 5 N/Wb
B. 25 N/Wb
C. 125 N/Wb
D. 0.2 N/Wb
286. The relative permeability of a magnetic material is 10^5. What is its permeability?
A. 4π × 10^5 H/m
B. 4π × 10^-12 H/m
C. 4π × 10^-2 H/m
D. 4π × 10^-7 H/m
287. Which of the following has the highest permeability?
A. Soft iron
B. Steel
C. Air
D. Permalloy
288. A magnetic pole produces 5000 field lines. How much is the flux in webers?
A. 50 × 10^-6
B. 5 × 10^-6
C. 500 × 10^-6
D. 500 × 10^-5
289. As the magnetic intensity decreases, the relative permeability of a magnetic material
A. decreases
B. remains the same
C. increases
D. becomes zero
290. The permeability of a material having a flux density of 5 Wb/m^2 is 10^-5 H/m. What is the value of magnetizing force?
A. 5 × 10^-5 N/Wb
B. 500 × 10^3 N/Wb
C. 4π × 10^-7 N/Wb
D. 4π × 10^7 N/Wb
291. When the relative permeability of a material is slightly less than 1, it is called _____ material.
A. diamagnetic
B. ferromagnetic
C. paramagnetic
D. non-magnetic
292. When the relative permeability of a material is slightly more than 1, it is called ______ material.
A. diamagnetic
B. ferromagnetic
C. paramagnetic
D. non-magnetic
293. Which of the following is a diamagnetic material?
A. Aluminum
B. Silver
C. Air
D. Cobalt
294. Which of the following is a paramagnetic material?
A. Carbon
B. Bismuth
C. Copper
D. Oxygen
295. The greater percentage of materials is _________.
A. diamagnetic
B. paramagnetic
C. ferromagnetic
D. non-magnetic
296. When the relative permeability of a material is much greater than 1, it is called _______ material.
A. diamagnetic
B. ferromagnetic
C. paramagnetic
D. non-magnetic
297. The flux density in an air-cored coil is 10^-3 Wb/m^2. With a cast iron core of relative permeability 100 inserted, the flux density will become
A. 10^-3 Wb/m^2
B. 10^-2 Wb/m^2
C. 10^3 Wb/m^2
D. 0.1 Wb/m^2
298. At/m is a unit of
A. mmf
B. magnetic force
C. reluctance
D. magnetic flux density
299. The direction of force o a current carrying conductor placed in a magnetic field can be found by
A. Cork screw rule
B. Fleming’s left hand rule
C. Fleming’s right hand rule
D. using a compass
300. When a current carrying conductor is placed in a magnetic field, the maximum force will act on the conductor when the conductor is at an angle of _______ to the magnetic field.
A. 45°
B. 60°
C. 30°
D. 90°
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